Evaluation of post-fabrication thermoforming process for intracortical Parylene sheath electrode

The chemical, mechanical, and electrochemical attributes of the Parylene sheath electrode (PSE) were evaluated following a post-fabrication thermoforming process to determine its impact on both the polymer and thin film platinum materials. The three-dimensional conical shape of the PSE was formed via thermal molding of a surface micromachined Parylene C microchannel using a custom shape-forming microwire having the desired taper at 200°C for 48 hours under vacuum. Contact angle and Fourier transform infrared spectroscopy measurements indicated that the thermoforming process resulted in no significant changes to the surface and bulk chemistry of Parylene. The thermoformed Parylene samples possessed greater Young´s modulus, but retained their flexibility. Electrochemical characterization of electrodes before and after thermoforming revealed a decreased storage charge capacity and increased electrode impedance, however, recording functionality was not lost as resolvable neuronal unit activity was successfully obtained post-implantation.